Method for reducing intraocular pressure in the mammalian eye by administration of chloride channel blockers

ABSTRACT

Pharmaceutical compositions and a method are disclosed for treating glaucoma and/or ocular hypertension in the mammalian eye by administering to the mammalian eye the pharmaceutical composition of the invention which contains, as the active ingredient, one or more compounds having chloride channel blocking activity. Examples of chloride channel blockers utilized in the pharmaceutical composition and method of treatment are: ##STR1## wherein R is hydrogen or a pharmaceutically-acceptable cation, e.g. an alkali or alkaline earth metal, or a quaternary amine; or R represents a ester-forming moiety, e.g. a lower alkyl radical, having up to six carbon atoms, that may be derived from a lower alkanol.

This application is a continuation of application Ser. No. 08/346,660,filed Nov. 30, 1994, now U.S. Pat. No. 5,559,151.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention is directed to pharmaceutical compositions, andprimarily to topically applied ophthalmic compositions comprising as theactive ingredient one or more compounds having the ability to blockchloride channels in the ciliary epithelium, e.g. to inhibit thetransport of chloride ions and fluid secretion in epithelia. Thepharmaceutical compositions are useful for reducing intraocular pressurein animals of the mammalian species. In another aspect, the presentinvention is directed to administering such formulations andcompositions to animals of the mammalian species (including humans) forreducing intraocular pressure in the eye.

2. Brief Description of the Art

Glaucoma is an optical neuropathy associated with elevated intraocularpressures which are too high for normal function of the eye, and resultsin irreversible loss of visual function. It is estimated in medicalscience that glaucoma afflicts approximately 2 per cent of thepopulation over the age of forty years, and is therefore a serioushealth problem. Ocular hypertension, i.e. the condition of elevatedintraocular pressure, which has not yet caused irreversible damage, isbelieved to represent the earliest phase of glaucoma. Many therapeuticagents have been devised and discovered in the prior art for thetreatment or amelioration of glaucoma and of the condition of increasedintraocular pressure which precedes glaucoma.

The drugs currently utilized in the treatment of glaucoma includemiotics (e.g., pilocarpine, carbachol, and acetylcholinesteraseinhibitors), sympathomimetrics (e.g., epinephrine anddipivalylepinephrine), beta-blockers (e.g., betaxolol, levobunolol andtimolol), alpha-2 agonists (e.g., para-amino clonidine) and carbonicanhydrase inhibitors (e.g., acetazolamide, methazolamide andethoxzolamide). Miotics and sympathomimetics are believed to lowerintraocular pressure by increasing the outflow of aqueous humor, whilebeta-blockers, alpha-2 agonists and carbonic anhydrase inhibitors arebelieved to lower intraocular pressure by decreasing the formation ofaqueous humor. All five types of drugs have potential side effects.Miotics, such as pilocarpine, can cause blurring of vision and othervisual side effects which may either decrease patient compliance orrequire termination of miotic drug therapy. Carbonic anhydraseinhibitors can also cause serious side effects which affect patientcompliance and/or necessitate withdrawal of the drug therapy. At leastone beta-blocker, timolol, has increasingly become associated withserious pulmonary side effects attributable to its effect on beta-2receptors in pulmonary tissue.

As a result additional antiglaucoma drugs are being developed, e.g.,prostaglandin derivatives, muscarinic antagonists, etc.

In light of the foregoing circumstances, it is clear that a need existsfor new, more potent antiglaucoma compositions which avoid or reduce theabove-cited side effects and enhance patient compliance, since theforegoing and other anti-glaucoma and ocular hypotensive compounds andagents of the prior art do not provide a treatment or cure for glaucomaand ocular hypertension which is satisfactory in all respects.Therefore, the pharmacological and related arts and sciences continuesearching for additional and better anti-glaucoma and ocular hypotensiveagents.

Chloride channel blockers such as 5-nitro-2-(3-phenylpropylamino)-benzoate (NPPB) have been shown to inhibit Cl⁻transport and fluid secretion/absorption in rat intestine. (See forexample, Acta Physiol Scand: No. 149, 1993: pp. 365-376, Fryklund etal., "The effects of chloride transport inhibitors on intestinal fluidand ion transport in vivo and in vitro".)

SUMMARY OF THE INVENTION

Surprisingly it has been discovered in accordance with the presentinvention that chloride channel blockers are effective as anti-glaucomaagents and as agents for reducing intraocular pressure, when such agentsare applied to the mammalian eye in a pharmaceutical composition,preferably in a topical ophthalmic composition. Accordingly, the presentinvention relates to a method of treating glaucoma, or ocularhypertension by topically administering to the mammalian eye anophthalmic composition which contains an effective amount of a chloridechannel blocker. A preferred example of chloride channel blockerssuitable as the active ingredients of the ophthalmic compositions of theinvention are: ##STR2## wherein R is hydrogen or apharmaceutically-acceptable cation, e.g. an alkali ion, or a quarternaryamine; or R represents a ester-forming moiety, e.g. a lower alkylradical, having up to six carbon atoms, i.e. a radical that may bederived from a lower alkanol.

While not wishing to be bound by theory it is believed that in ciliaryepithelium, i.e. the tissue mediating aqueous humor secretion, movementof fluid info the aqueous chamber, is in part orchestrated by K⁺ and Cl⁻channels residing in the non-pigmented ciliary epithelial (NPE) cells.(See for example, American Journal of Physiology, 1994, Vol. 0363-6143,pp C1210-C-1221, Edelman et al, "Ion transport asymmetry and functionalcoupling in bovine pigmented and nonpigmented ciliary epithelialcells".) Thus, aqueous secretion is inhibited and hence intraocularpressure (IOP) is lowered by blocking Cl⁻ channels in the NPE cells.

The ophthalmic compositions of the invention contain the activeingredient in a concentration range of approximately 0.0001 to 0.1 percent weight by volume. The composition itself includes, in addition tothe active ingredient, such excipients which are per se well known inthe art for preparing ophthalmic compositions, particularly ophthalmicsolutions. In accordance with the method of the invention the ophthalmiccompositions, preferably ophthalmic solutions are applied topically tothe mammalian eye approximately 1 or 2 times daily.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the effect of the presence of the drug NPPB onthe regulatory volume decrease (RVD) of a suspension of cultured humannon-pigmented ciliary epithelial (NPE) cells.

FIG. 2 is a graph showing the effect of intracameral administration ofthe drug NPPB on the intraocular pressure (IOP) in the rabbit eye.

DETAILED DESCRIPTION OF THE INVENTION

The compounds which are utilized in accordance with the method of thepresent invention, and in the pharmaceutical compositions of the presentinvention, are chloride channel blockers. In this regard the termchloride channel blocker is defined as those compounds or agents whichinhibit net Cl flux (current) through a Cl specific pathway (channel,integral membrane protein) within biological membranes. Specific andpreferred examples of chloride channel blockers which are utilized inaccordance with the present invention are provided below.

Pharmaceutically acceptable salts of the chloride channel blockers canalso be used in accordance with the present invention. Apharmaceutically acceptable salt may be any salt which retains theactivity of the parent compound and does not impart any deleterious oruntoward effect on the subject to which it is administered and in thecontext in which it is administered.

Such a salt may be derived from any organic or inorganic acid or base.The salt may be a mono or polyvalent ion. Of particular interest wherethe acid function is concerned are the inorganic ions, such as alkaliions, e.g. sodium, potassium, etc. Organic amine salts may be made withmines, particularly ammonium salts such as mono-, di- and trialkylamines, e.g. alkyl amines wherein each alkyl group may comprise up tosix carbon atoms, or ethanol amines. Salts may also be formed withcaffeine, tromethamine and similar molecules. It is only important thatthe cation of any salt of a chloride channel blocker utilized in thecompositions or methods of this invention be able to block chloridechannels in the ciliary epithelium.

For reducing intraocular pressure in a mammalian eye, and particularlyfor treatment of glaucoma in humans suffering from that condition, theactive compounds (or mixtures or salts thereof) are administered inaccordance with the present invention to the eye admixed with anophthalmically acceptable carrier. Any suitable, e.g., conventional,ophthalmically acceptable carrier may be employed. A carrier isophthalmically acceptable if it has substantially no long term orpermanent detrimental effect on the eye to which it is administered.Examples of ophthalmically acceptable carriers include water (distilledor deionized water), saline and other aqueous media. In accordance withthe invention, the active compounds are preferably soluble in thecarrier which is employed for their administration, so that the activecompounds are administered to the eye in the form of a solution.Alternatively, a suspension of the active compound or compounds (orsalts thereof) in a suitable carrier may also be employed.

In accordance with the invention the active compounds (or mixtures orsalts thereof) are administered in an ophthalmically acceptable carrierin sufficient concentration so as to deliver an effective amount of theactive compound or compounds to the eye. Preferably, the ophthalmic,therapeutic solutions contain one or more of the active compounds in aconcentration range of approximately 0.0001% to approximately 1% (weightby volume) and more preferably approximately 0.0005% to approximately0.1% (weight by volume).

Any method of administering drugs directly to a mammalian eye may beemployed to administer, in accordance with the present invention, theactive compound or compounds to the eye to be treated. By the term"administering directly" is meant to exclude those general systemic drugadministration modes, e.g., injection directly into the patient's bloodvessels, oral administration and the like, which result in the compoundor compounds being systemically available. The primary effect on themammal resulting from the direct administering of the active compound orcompounds to the mammal's eye is preferably a reduction in intraocularpressure. More preferably, the active useful compound or compounds areapplied topically to the eye or are injected directly into the eye.Particularly useful results are obtained when the compound or compoundsare applied topically to the eye in an ophthalmic solution, i.e. asocular drops.

Topical ophthalmic preparations, for example ocular drops, gels orcreams, are preferred because of ease of application, ease of dosedelivery and fewer systemic side effects, such as cardiovascularhypotention. An exemplary topical ophthalmic formulation is shown belowin Table I. The abbreviation q.s. means a quantity sufficient to effectthe result or to make volume.

    ______________________________________                                        Ingredient            Amount (% W/V)                                          ______________________________________                                        Active Compound in accordance                                                                       about 0.0001 to                                         with the invention,   about 1                                                 Preservative          0-0.10                                                  Vehicle               0-40                                                    Tonicity Adjustor     1-10                                                    Buffer                0.01-10                                                 pH Adjustor           q.s. pH 4.5-7.5                                         antioxidant           as needed                                               Purified Water        as needed to                                                                  make 100%                                               ______________________________________                                    

Various preservatives may be used in the ophthalmic preparationdescribed in Table I above. Preferred preservatives include, but are notlimited to, benzalkonium chloride, chlorobutanol, thimerosal,phenylmercuric acetate, and phenylmercuric nitrate. Likewise, variouspreferred vehicles may be used in such ophthalmic preparation. Thesevehicles include, but are not limited to, polyvinyl alcohol, povidone,hydroxypropyl methyl cellulose, poloxamers, carboxymethyl cellulose andhydroxyethyl cellulose.

Tonicity adjustors may be added as needed or convenient. They include,but are not limited to, salts, particularly sodium chloride, potassiumchloride etc., mannitol and glycerin, or any other suitableophthalmically acceptable tonicity adjustor.

Various buffers and means for adjusting pH may be used so long as theresulting preparation is ophthalmically acceptable. Accordingly, buffersinclude but are not limited to, acetate buffers, titrate buffers,phosphate buffers, and borate buffers. Acids or bases may be used toadjust the pH of these formulations as needed.

In a similar vein, ophthalmically acceptable antioxidants include, butare not limited to, sodium metabisulfite, sodium thiosulfate,acetylcysteine, butylated hydroxyanisole, and butylated hydroxytoluene.

The ophthalmic solution (ocular drops) may be administered to themammalian eye as often as necessary to maintain an acceptable level ofintraocular pressure in the eye. In other words/the ophthalmic solution(or other formulation) which contains the chloride channel blocker asthe active ingredient, is administered to the mammalian eye as often asnecessary to maintain the beneficial hypotensive effect of the activeingredient in the eye. Those skilled in the art will recognize that thefrequency of administration depends on the precise nature of the activeingredient and ifs concentration in the ophthalmic formulation. Withinthese guidelines it is contemplated that the ophthalmic formulation ofthe present invention will be administered to the mammalian eyeapproximately once or twice daily.

Specific examples of chloride channel blockers which are used as theactive effective ingredients in the ophthalmic compositions of thepresent invention are described and shown below: N-phenylanthranilicacid, DPC (diphenylamine-2-carboxylic acid), IAA-94(R(+)-methylindazone, indanyloxyacetic acid 94), 2-aminomethyl phenolssuch as MK-447 (2-aminomethyl-4-(1,1-dimethyl ethyl)-6-iodophenolhydrochloride (2) disulfonic stilbenes such as DIDS(4,4'-diisothiocyanostilbene-2-2'-disulfonic acid).

Alternatively, a chloride channel blocker may be defined as apharmaceutical compound showing activity in the following assay:

Inhibition of current mediated by Cl ions using patch clamp technologyin the whole cell, cell attached or cell excised mode. (See for example,Biochimica et al Biophysica Acta, Vol. 947, 1988, pp. 521-547, Gogelein,H., "Chloride channels in epithelia".)

EXAMPLES

The present invention is demonstrated by in vitro and in vivo data. InFIG. 1, 5 μM NPPB were found to depress the regulatory volume decrease(RVD) that occurs following hyposmotic swelling of cultured humannon-pigmented ciliary epithelial (NPE) cells. In this example, NPE cellswere suspended in an isosmotic (290 mOsm) solution containing 5 μM NPPBfor 30 minutes prior to suspension in a hyposmotoic (198 mOsm) solution.Control cells were subjected to the same hyposmotic solution but withoutNPBB in the medium. Changes in cell volume were measured using a CoulterCounter interfaced to a Coulter Channelyzer. It is noted that, followingosmotic swelling, control cells regulate towards their originalisosmotic volume while NPBB-treated cells remain swollen. The abovefindings indicate that intracellular NPBB, via blocking of the chloridechannel, inhibits solute and osmotically obliged H₂ O efflux. Becausethe chloride-dependent ion flux pathways, activated following osmoticcell swelling of NPE cells, are involved in aqueous secretion, NPBB willinhibit aqueous humor formation and, thus, lower IOP.

In the in vivo studies normotensive rabbits were injected intracamerallywith 100 μM NPBB. FIG. 2 shows that 100 μM NPBB lowered IOF by 7 mm ofHg and IOP remained depressed for 24 hours. Taken together, the above invitro and in vivo experiments demonstrate that blocking the chloride ionchannel in the ciliary epithelium will reduce IOP.

One advantage Cl⁻ channel inhibition has over other IOP loweringtherapies is that the effector, i.e. the ion channel, is targeted ratherthan the receptor. Since effector blockage is direct, it should be themost potent and effective way of inhibiting aqueous secretion and hencelowering IOP. On the other hand, targeting a receptor to block aneffector is indirect and relies on modulation of a series of cellularevents (intracellular messengers/signals) prior to effector inhibition.

In view of the above, it is clear that the scope of the presentinvention should be interpreted solely on the basis of the followingclaims, as such claims are read in light of the disclosure.

What is claimed is:
 1. A method of treating animals of the mammalianspecies for glaucoma which comprises administering to the eye of amammal having glaucoma a pharmaceutical composition comprising as itsactive ingredient one or more compounds having chloride channel blockingactivity.
 2. A method of claim 1 wherein the composition is anophthalmic solution, adapted for administration to the eye of a mammalin the form of eye droplets.
 3. The method of claim 2 wherein thecompound having chloride channel blocking activity is present in theconcentration range of 0.0001 to 1 per cent by volume.
 4. The method ofclaim 1 wherein the compound having chloride channel blocking activityis selected from the group consisting of N-phenylanthranilic acid, DPC(diphenylamine-2-carboxylic acid), IAA-94 (R(+)methylindazone,indanyloxyacetic acid 94), 2-aminomethyl phenols, MK-447(2-aminomethyl-4-(1,1-dimethyl ethyl)-6-iodophenol hydrochloride (2)disulfonic stilbenes and DIDS(4,4'-diisothiocyanostilbene-2-2'-disulfonic acid) and 5-nitro-2(3phenyl propyl amino)-benzoate (NPPB).
 5. The method of claim 1 whereinthe compound having chloride channel blocking activity is selected fromthe group consisting of compounds represented by the formula: ##STR3##wherein R is hydrogen or a pharmaceutically-acceptable cation.
 6. Themethod of claim 5 wherein R is hydrogen or an alkali metal ion or aquaternary amine selected from the group consisting of mono-, di- andtrialkyl amines, wherein each alkyl group may comprise up to six carbonatoms, ethanolamine, or caffeine or tromethamine, or a lower alkylradical having up to six carbon atoms.
 7. The method of claim 6 wherethe composition is an ophthalmic solution, adapted for administration tothe eye of a mammal in the form of eye droplets.
 8. The method of claim7 wherein the composition contains approximately 0.0001 to 1 per centweight by volume of said compound having chloride channel blockingactivity.
 9. The method of claim 1 wherein the compound having chloridechannel blocking activity is selected from the group consisting ofMK-447 (2-aminomethyl-4-(1,1-dimethyl ethyl)-6-iodophenol and DIDS(4,4'-diisothiocyanostilbene-2-2'-disulfonic acid).
 10. A method oftreating animals of the mammalian species, including humans, for thepurpose of reducing intraocular pressure in the eye of the mammalcomprising the step of administering to the mammal a pharmaceuticalcomposition which comprises as its active ingredient one or morecompounds having chloride channel blocking activity.
 11. The method oftreatment of claim 10 where the composition is an ophthalmic solutionadapted for administration to the eye of a mammal in the form of eyedroplets.
 12. The method of treatment of claim 11 wherein in theophthalmic composition the concentration of the compound having chloridechannel blocking activity is in the range of approximately 0.0001 to 1per cent weight by volume.